This invention relates to a semiconductor device and to a method of manufacturing a semi-insulating layer therefor, and in particular, relates to semiconductor devices such as diodes, transistors or resistors which has one or more surface passivating layers, and to a method of manufacturing the same.
Conventional passivating layers include a SiO.sub.2 layer, a glass layer with phosphorus, and a Si.sub.3 N.sub.4 layer. In the case of SiO.sub.2 layer, electric charges are induced at a surface of a semiconductor substrate by electric charges in the SiO.sub.2 layer, which are fixed by the polarization in a molding resin, and it deteriorates the breakdown voltage and the reliability influenced by an external electric field. The above passivating layers have a bad water-resisting property, where the leakage current varies according to humidity conditions.
A pure polycrystalline silicon layer was also proposed for passivation, but it has a large leakage current and a small DC current gain h.sub.FE, while it has a high breakdown voltage.
Matsushita et al applications, Ser. Nos. 561,532 (now U.S. Pat. No. 4,014,037) and 624,889, filed on Mar. 24, 1975 and Oct. 22, 1975, respectively, and assigned to the same assignee as the present invention, disclose a polycrystalline silicon layer with oxygen atoms and/or nitrogen atoms for passivation, where the resistance of the polycrystalline silicon layer is semi-insulating in character, having a resistivity of approximately 10.sup.7 to 10.sup.11 ohm-cm, and the breakdown voltage and the reliability from resistance to water are improved. This layer was provided not only for passivation, but also for the formation of a resistor or the like.
This polycrystalline silicon layer is uniformly formed by a chemical vapor deposition, in which silicon is deposited by a thermal decomposition of SiH.sub.4 and oxygen or nitrogen is doped in silicon by a decomposition of nitrogen oxide (N.sub.2 O, etc.) or NH.sub.3, respectively. This method is suitable for a uniform passivating layer, but it is difficult to control the gas flow rate and temperature to determine the oxygen or nitrogen concentration, to form a layer selectively or to vary the concentration profile laterally.